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参数资料
| 型号： | RP502L081B-TR |
| 厂商： | RICOH COMPANY LTD |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING REGULATOR, 3960 kHz SWITCHING FREQ-MAX, PDSO6 |
| 封装： | 1.60 X 1.60 MM, HALOGEN FREE AND ROHS COMPLIANT, DFN-6 |
| 文件页数： | 4/30页 |
| 文件大小： | 1222K |
| 代理商： | RP502L081B-TR |
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RP502x
12
Operation of step-down DC/DC converter and Output Current
The step-down DC/DC converter charges energy in the inductor when the Lx transistor is turned on, and
discharges the energy when the Lx transistor is turned off. The step-down DC/DC converter also controls with
the less energy loss and supplies the lower output voltage than the input voltage. The operation of the DC/DC
converter will be explained with the following diagrams:
<Basic Circuit>
<Inductor Current >
Pch Tr
L
Nch Tr
VIN
i1
VOUT
CL
i2
GND
T＝1/fosc
ton
toff
topen
ILmin
ILmax
IL
i1
i2
Step 1: Pch Tr. turns on and current IL (=i1) flows. Then, L and CL are charged with energy. At this moment, IL
(=i1) increases from ILmin (=0) to ILmax in proportion to the On-time period (ton) of Pch Tr.
Step 2: When Pch Tr. turns off, Synchronous rectifier Nch Tr. turns on and IL(=i2) flows in order to maintain IL
at ILmax.
Step 3: IL (=i2) starts to decrease gradually when topen time period starts. IL reaches to ILmin (IL=ILmin=0)
when topen time period ends and then Nch Tr. turns off. In the continuous mode, toff time period runs
out before IL becomes ILmin (IL=ILmin=0). The next cycle starts. Pch Tr. turns on and Nch Tr, turns off.
Since toff time period runs out before IL becomes ILmin (IL=ILmin=0), ILmin (>0) is still remaining. In
this case, IL starts increasing from ILmin (>0).
In the case of PWM control system, the output voltage is maintained constant by keeping the switching time
(fosc) per unit constant, and by controlling the On-time period (ton).
When the step-down operation is constant and stable, as shown in the above “Inductor Current”, the maximum
inductor current (ILmax) will be same as the on-time period of Pch Tr. (ton) and the minimum inductor current
(ILmin) will be same as the on-time period of Pch Tr. (toff).
The difference between ILmax and ILmin is described as
ΔI:
I = ILmax – ILmin = VOUT x topen / L = (VIN – VOUT) x ton / L ....................................Equation 1
Wherein,
T = 1 / fosc = ton + toff
duty (%)= ton / T x 100 = ton x fosc x 100
topen <
= toff
In Equation 1, “VOUT x topen / L” shows the amount of current change at the on-time. “(VIN – VOUT) x ton / L”
shows the amount of current change at the off-time”.
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